Help!! What is this?

Just looks like diotoms to me. I'm on my phone so maybe I'm not seeing something.

 

That's what I thought too, diatoms. Looks pretty yellow though. Is it loose on the rock and substrate? Looks like its more "grown" onto the rocks. Have you tried anything to remove it?

 

Looks like diatoms to me too

 

Wait to add your snails and other inverts until you are sure your tank is cycled and water params are good otherwise they will prob die.

 

That looks like a fresh startup. The tank is cycling and at this point the diatoms take over (for now).

Best advice is to have patience and enjoy the ugly tank syndrome they all have when new. I soaked my power heads in vinegar to clean them off and When I returned them to the tank they got a dusting of diatoms for a couple days.

Stay away from aditives that promise miracles. People have crashed their tanks with stuff like purple up. Test for ammonia, wait two weeks the add a pair of hearty fish and a pair of hearty shrimp, or other invertebrate. Use frozen ocean based foods and/or quality pellets. no flakes! Test and test for ammonia nitrite and nitrate. Read up on them and always have a batch of water mixed up for emergencies. Never use freshly mixed salt that has been mixed less than an 3 hoursalways acclimate and quarantine new arrivals. I prefer drip method but bag float works too.

Be prepared to fail. It's inevitable so keep it cheap. Don't start with a 60$ powder brown tang.